A flip chip is generally a monolithic semiconductor device, such as an integrated circuit (IC), having bead-like terminals formed on one of its surfaces. The terminals, also referred to as solder bumps, serve to both secure the chip to a circuit board and electrically interconnect the flip chip circuitry to a conductor pattern formed on the circuit board, which may be a ceramic substrate, printed wiring board, flexible circuit, or a silicon substrate. Due to the numerous functions typically performed by the microcircuitry of a flip chip, a relatively large number of solder bumps are often required. The solder bumps are typically located at the perimeter of the flip chip on electrically conductive pads that are electrically interconnected with the circuitry on the flip chip. The size of a typical flip chip is generally on the order of a few millimeters per side, resulting in the solder bumps being crowded along the perimeter of the flip chip, with a typical solder bump pitch being about eight to ten mils (about 200 to about 250 micrometers). As a result, flip chip conductor patterns are typically composed of numerous individual conductors that are often spaced apart about one millimeter or less.
Flip chips are widely used in the electronics industry as a result of their compact size. While typically mounted directly to a substrate, flip chips have been incorporated into packages, an example of which is ball grid array (BGA) packages. BGA's typically have an IC chip that is wire bonded to a "daughter" circuit board with wires that are routed through the daughter board to terminals, or pads, on the opposite surface of the daughter board. Similar to the flip-chip process, the pads form a pad pattern and serve as interconnects between the IC chip and a conductor pattern on a mother board to which the BGA package is mounted. Where flip chips are used in a BGA package to form a multi-chip module, one or more flip chips are mounted to a high-density circuit board, which is then mounted within the BGA package, with interconnections made to the pad pattern of the package. Yet other prior art multi-chip modules have employed multiple flip chips that are mounted to a single circuit board or substrate, which is then wire bonded to a mother board.
While the above packaging techniques are able to capitalize on the processing and assembly advantages provided by flip chips, further improvements in packaging density are continuously sought.